1. Field of the Invention
This invention relates to machines for cleaning carpets, draperies, upholstery, and the like and finds particular application in such machines where hot cleaning liquids are sprayed onto the surface and then removed by suction.
2. Description of the Prior Art
The prior art includes various types of cleaning machines with various types of liquid heating apparatus. In a common type of system, two general types of cleaning liquids can be used in the same machine: aqueous detergent cleaning solutions which can safely be heated to 200.degree. F. and mineral spirit cleaning solvents which can become dangerously volatile at various lower temperatures depending upon the composition and concentration.
Because this type of fabric cleaning device works best when the liquid is at the highest temperature possible, it becomes necessary to operate the machine at different temperatures for different cleaning liquids. An aqueous-based detergent may be safely and effectively heated to a temperature of 200.degree. F., but it is extremely dangerous to attempt heating a mineral spirits solution with a flash point of 140.degree. F. to that temperature. Clearly there is a need for temperature limiting devices.
Prior art cleaning machines usually provide either a manually operated switch to choose between a finite number of temperatures or a manually operated dial from which any temperature in a range can be selected. While these machines are adequate if used correctly, it is possible that a machine operator sometimes using solvents and sometimes aqueous-based detergents in the same machine may inadvertently attempt to heat the solvent to an unsafe temperature.